In recent years there have been an increase in attempts, depending on the traffic and technical conditions of the rail vehicles in the various parts of cities, to combine the possibilities and properties of streetcars and subways in the same vehicles.
This requires entry steps for two different platform heights. As a rule, entry and exit on the streetcar routes are from and to a sidewalk or a sidewalk-like island using a stairway that is part of the vehicle; while on the subway routes there are high railway platform without any real step.
Movable steps are known, where the step-plate parts, which in their initial position comprise a part of the vehicle floor, go through an unfolding motion while being lowered. Riders, who mistakenly stand either entirely or partly on this plate, are thus exposed to an immediate danger of accident by either twisting an ankle or slipping outward on the slanting plate. Also, the devices used heretofore require a large amount of space in the direction of the width of the vehicle, so that problems result in mounting the apparatus below the vehicle floor between the step arrangements.
A further disadvantage of the previous systems and proposals used up to now consists of the fact that in the under-way position there are niches where, for example, snow can accumulate, or where special, movable covering aprons are additionally required.